The present invention relates to a sequential driving method of a heat element array having a function to self-regulate a heat amount of each heat element.
Conventionally, there has been utilized generally the block-divisional driving method to drive a thermal head comprised of a plurality of heat resistive elements in order to reduce power consumption. Namely, M.times.N number of the heat elements are divided into N number of blocks each containing M number of the heat elements. The respective blocks are driven in sequential manner.
There has been proposed another conventional method of controlling a number of heat elements to be driven concurrently. Namely, prior to application of a selection signal effective to determine selective driving and nondriving of the plurality of heat elements, the number of heat elements to be driven is counted provisionally. If the counted number exceeds a predetermined maximum limit number of heat elements which are allowed to driven concurrently, a part of all the selected heat elements is first driven at once. Then, the remaining selected heat elements are driven to thereby avoid exceeding the predetermined maximum limit number.
However, with regard to the conventional block-divisional driving method, the number of blocks should be increased so as to efficiently reduce a capacity of a power source. Such increase in the block number may disadvantageously increase a number of strobe signals used to time the driving of the blocks. Further, if each block is sequentially driven by mechanical means, a respective block may be unnecessarily strobed even if that block is not selected entirely for dot printing, thereby disadvantageously causing a loss time due to unnecessary strobe to an entirely nonselected block. Further, the electric power source must have a capacity sufficient to cover a maximum electric power output which occurs when all of the heat elements are turned on within one block, even though such a case occurs infrequently. Consequently, the capacity of the power source is not utilized efficiently.
With regard to the conventional drive number control method, it is necessary to provide a counter and to regularly adjust the selection signal for the predetermined maximum limit number, whereby a CPU is heavily involved in this adjustive control work requiring fast processing speed.